With the increase in demands for communication using broadband, a user-oriented access line has been shifted to a large capacity access line using an optical fiber instead of an access technique which is based on a telephone line such as a Digital Subscriber Line (DSL). Currently, a Passive Optical Network (PON) system (hereinafter, referred to as a PON simply, an optical passive network system, or a passive optical network system in some cases) is frequently used for an access line service in terms of line construction costs and maintenance and management costs. For example, standardization in International Telecommunication Union Telecommunication Standardization Sector (ITU-T) is a representative example. The Western countries have started to introduce Gigabit PON (GPON) since around 2006.
With the increase in opportunities for home users (communication service subscribers) to access the Internet and collect information or use information services required for social lives, there have been requests for preparation for communication networks, particularly, completion of access network providing services which connect subscribers to communication networks. That is, carriers, which provide the communication networks, are required to increase capital for increasing the number of users accommodated in each station along with an increase in the number of users of access lines. In order to increase the number of users, a method of additionally introducing the PON or of increasing the number of users accommodated in each PON system has been examined. In relation thereto, next generation PON techniques called 10 Gigabit PON (10GPON) and 10 Gigabit Ethernet (registered trademark) PON (10GEPON) have been examined as means for performing transmission at a higher bit rate than in the related art in ITU-T and Institute of Electrical and Electronics Engineers (IEEE).
The above-described subscriber accommodation equipment is installed in a building of a communication carrier. In order to relay a connection between a subscriber and an opposite device (another user, a web server, or the like), typically, there is a network configuration in which a signal from a subscriber is input to a relay transmission network (hereinafter, referred to as a relay network in some cases) from the subscriber accommodate equipment, and, simultaneously, a signal is transferred in an opposite direction to the signal, and thereby the user can obtain information. The relay network is connected to provider networks or core networks, and plays a role of distributing a user signal to one or more provider networks or core networks and transferring a signal from the provider networks or the core networks to the user in a reverse direction. This relay network is called an access network or a backhaul.
Although a dedicated line service using an Asynchronous Transfer Mode (ATM), frame relay, SONET/SDH, or the like is frequently used for a user network in the related art, recently, a low-priced packet communication network exemplified by Ethernet (registered trademark) has been frequently used with an increasing request for cost reduction and the progress of a communication technique and a device manufacturing technique which can handle expanded transmission capacity. On the other hand, SONET/SDH is the mainstream as a communication technique inside a core network, and forms a large capacity and high reliability network in order to transmit data which is collected via a plurality of access networks.
In recent years, along with becoming widespread of the Internet, a packet (or also referred to as a frame) communication technique exemplified by Ethernet (registered trademark) and Multi Protocol Label Switching (MPLS) has progressed and attracted attention as a base technique for forming a communication network. Features of the packet network lie in ease of handling or reduction in development (introduction) costs. In addition thereto, circumstances in which a standard technique which targets a packet communication technique and is related to maintenance and management is being established are main causes for the communication carriers to introduce and expand the packet communication technique. Definition or the like of the above-described maintenance and management function or a function of the packet communication network has been discussed in the standardization groups such as ITU-T, IEEE, and The Internet Engineering Task Force (IETF).